1. Field of the Invention
The present invention concerns a hearing device of the type having at least one housing part wearable behind the ear, an ear fitting piece wearable in the ear, an earpiece tube connecting the housing part with the ear fitting piece, a microphone for acquisition of an acoustic input signal and emission of an electrical input signal, a signal processing and amplifier unit for processing and amplification of the electrical input signal and for emission of an electrical output signal, and an earpiece arranged in the ear fitting piece for transducing of the electrical input signal into an acoustic output signal. The invention also concerns an earpiece tube for such a hearing device.
2. Description of the Prior Art
In a behind-the-ear hearing device with a housing part that can be worn behind the ear and an ear fitting piece (otoplastic) wearable in the ear, the sound is transported from the hearing device into the ear of the patient through an earpiece tube. For a behind-the-ear hearing device equipped with an (external) earpiece arranged in the ear fitting piece, the electrical conductor with which the earpiece is coupled to the hearing device runs through the earpiece tube.
Since the hearing device, including earpiece tube and possibly the earpiece or otoplastic, abuts the body of the hearing device user, structure-borne sound can be transferred from the hearing device user to the hearing device. The coupling of the structure-borne sound ensues either directly from the body of the hearing device user to the hearing device itself, or via the earpiece or the earpiece tube to the hearing device, caused by vibrations of the earpiece or other events. The structure-borne sound can conversely also propagate from the hearing device via the earpiece tube and the earpiece or, respectively, the otoplastic to the ear. In each case the injected structure-borne sound adulterates the usable signal.
Hearing devices wearable behind the ear with an earpiece in the ear fitting piece, known as RIC (receiver in canal) devices, are prone to feedback in spite of the relatively large separation between the earpiece and the microphone. This results from the (often relatively rigid) connection of the hearing device housing with the ear fitting piece through which the vibrations of the earpiece are mechanically coupled back via the earpiece tube.
Moreover, mechanical feedbacks also increasingly occur in behind-the-ear hearing devices with an earpiece tube for sound conduction between the hearing device housing and the ear fitting piece, in which the earpiece tube also performs the function of a carrier that holds the hearing aid device behind the ear. Pre-formed earpiece tubes adapted to the anatomy of the ear are conventionally used for this purpose and must exhibit a specific rigidity for this purpose, and thus transfer mechanical vibrations (structure-borne sound) relatively well.
To avoid feedback it has previously been possible to reduce the effect of the structure-borne sound to the actual hearing device. For this purpose, the wall thickness of the housing of the hearing device is made as thick as possible in order to achieve an attenuating effect. Moreover, all internal mounting parts are designed such that they damp or filter out natural oscillations and structure-borne sound. Known measures for suppression of feedback in particular involve mounting or supporting the earpiece or the microphone in a vibration-damping manner.
By a reduced amplification or bandwidth, the feedback can be damped to a sufficient degree so that an electronic feedback compensator can prevent feedback whistling in the hearing device. More substantial, hearing losses, however, can then no longer be fully compensated.
A hearing device wearable behind the ear with an ear fitting piece that can be inserted into the auditory canal is known from DE 298 01 567 U1, in which the housing part wearable behind the ear and the ear fitting piece are connected with one another with a flexible carrying strap such that they can be detached. Together with jack bushing (receptacles) at the ear fitting piece and the housing part, jacks form detachable plug connectors for electrical and mechanical connection.
U.S. Pat. No. 6,766,030 discloses a hearing device wearable in the ear is known in which the earpiece is supported in a damping manner relative the housing of the hearing device such that mechanical vibrations transferred from the earpiece to the housing are attenuated.
A hearing device in which the earpiece emits neither structure-borne sound nor airborne sound to the microphone of the hearing device is known from DE 31 41 921 A1. For this purpose at least the housing of the earpiece is surrounded by a layer of foamed plastic with an air-tight outer skin.
Moreover, published European Application EP 1 484 943 A2 discloses a behind-the-ear hearing device that exhibits a one-part tubular shape as an external housing part. In the external housing part a speaker housing is held in rubber-elastic supports such that it can oscillate (vibrate) freely.
A hearing aid system in which the frequency response of the earpiece is influenced by the earpiece tube is also known from U.S. Pat. No. 6,275,596. For example, the tube tip can be provided with an acoustic damper in order to damp peaks in the frequency response of the earpiece.